EPA proposes guidance to handle herbicide-resistant weeds

WASHINGTON, June 8, 2016 - EPA is taking a “holistic”
approach to managing herbicide-resistant weeds, releasing new guidance last
week that the agency says is “intended to provide herbicide users and
registrants useful strategies that, when implemented, will slow herbicide
resistance and prolong the useful life of herbicides.”

Also, “unlike fungicides and insecticides, there have been
no new herbicide (modes of action, or MOAs) developed in the last 30 years,” the
guidance said. “Therefore, users do not have a new MOA to control
herbicide-resistant weeds and it’s important to protect the long term efficacy
of these chemistries.”

Glyphosate-resistant weeds are a particular problem. In
1988, glyphosate was applied to about 80 million acres, but by 2014, the total
acreage treated had increased to nearly 300 million acres. From 2010 to 2012,
the area of glyphosate-resistant weeds almost doubled, from 33 million acres to
over 61 million acres.

Glyphosate-resistant weeds can lighten farmers’ wallets.
USDA reported that in 2010, “growers with glyphosate-resistant weed problems
received over $67 per acre less for corn and over $23 per acre less for
soybeans due to increased costs to control weeds.” And in 2010 and 2011,
growers in Georgia spent over $100 million to control glyphosate-resistant Palmer
amaranth in cotton fields.

The guidance divides 28 MOAs into three categories of
concern (low, moderate, high) “based on the risk of developing
herbicide-resistant weeds.” MOAs associated with glyphosate, 2,4-D, atrazine
and glufosinate are classified as being of “high” concern.

The guidance includes 11 elements to be included in
herbicide resistance management and stewardship plans. Only the MOAs of high
concern would require all 11 elements.

EPA said in the guidance that it plans to implement
herbicide-resistance measures “for new herbicide active ingredients and new
uses of herbicides proposed for use on herbicide-resistant crops.”

EPA initially issued the draft herbicide resistance
management measures in its proposal to register new uses for dicamba-tolerant
cotton and soybeans, prompting the Weed Science Society of America (WSSA) and
affiliated groups, which commented on the guidance as part of that proposal, to
ask for a separate notice and comment period. EPA did so, and has asked for
comments on the two draft guidance documents by Aug. 2.

In its May 31 comments, WSSA said EPA should,
“for simplicity and to preserve the utility of all herbicides,” group all MOAs
together in one category of “resistance concern.”

One of the elements of a management plan (for moderate or
high-concern MOAs) would require herbicide registrants “to report new cases of
likely and confirmed resistance to EPA and users yearly.”

WSSA suggested EPA require reporting of two different
categories: suspected and confirmed cases. The association said that for
suspected cases, “It is vital to limit these reports to those evaluated by
trained experts and that they not include resistance reports from outside this
group.”

The “confirmed” category “would allow academics and industry
to provide scientific data confirming that a certain weed is resistant to a
specific herbicide,” WSSA said. “We feel that reports of new resistant species
for a given MOA should be confirmed by appropriate lab or greenhouse testing.”

“The National and Regional Weed Science Societies believe
that early reporting of suspected newly evolved resistance cases will be a
critical part of a plan to alert the agricultural community in time to increase
vigilance and institute mitigation measures before newly identified resistant
weed populations become widespread,” WSSA said.

WSSA was joined in its comments by the Aquatic Plant
Management Society, the Northeastern Weed Science Society, the North Central
Weed Science Society, the Southern Weed Science Society, and the Western
Society of Weed Science.

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